Chemosensory proteins used as target for screening behaviourally active compounds in the rice pest Cnaphalocrocis medinalis (Lepidoptera: Pyralidae)

Reverse chemical ecology based on insect functional odorant binding proteins has been extensively studied to screen behaviourally active compounds, whereas chemosensory proteins (CSPs), which are reportedly involved in olfactory chemical reception and could serve as molecular targets remain unclear. In the present study, two behaviourally active compounds for Cnaphalocrocis medinalis, a serious pest of rice in Asia, were successfully screened via an antenna-biased CSP, CmedCSP33. Fluorescence competitive binding assays showed that CmedCSP33 could bind to seven out of 32 rice volatiles. Fluorescence quenching experiments revealed that CmedCSP33 forms a stable complex with nerolidol and beta-ionone, and circular dichroism (CD) spectra demonstrated that these two compounds cause conformational changes in CmedCSP33. Furthermore, H-tube olfactometer bioassays showed that C. medinalis displayed prominent attractant responses to nerolidol and prominent repellent responses to beta-ionone. Additionally, binding assays and CD spectra at different pH values implied that extensive conformational changes may be a general feature of CSPs for triggering the subsequent chemical transduction. Overall, our findings provide evidence for the involvement of CSPs in olfactory perception, and a protocol for effectively screening behaviourally active compounds.